Impurities in zone-refining anthracene crystals

Abstract

Over the past five decades, paramount interest had been given to the synthesis of single crystals for use as scintillators in nuclear radiation detection field. Organic semiconductors are in principle less costly and of light weight, providing real potential as improved radiation detectors. However, challenges remain in the crystal growth and purification of the neutron detection material whereby the residual impurity will result in formation of excitation trap quenching the light yield within the host crystal. In this study, single crystals of anthracene up to 10 cm had been grown from the melt based on a self-designed, inexpensive and versatile zone refining apparatus. Platelets cut from these crystals by applying wire saw were tested for purity and perfection by Powder X-ray Diffraction (XRD), Laser Desorption Ionization-Time of Flight Mass Spectrometry (LDI-ToF MS), Fourier-Transform Infrared Spectroscopy (FT-IR), Atomic Force Microscopy (AFM) and fluorescence measurement. The results of characterization studies revealed that impurities within commercial anthracene powder such as carbazole and 9,9′bianthryl have been reduced effectively as indicated by LDI-ToF MS analysis. Meanwhile the photoluminescence analysis had clearly demonstrated higher photon energies derived from the pure crystal as compared to those of commercial material with higher content of impurities where free excitons during their localization surrender part of its energy to the surroundings.